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diff --git a/contrib/bind9/doc/draft/draft-daigle-napstr-04.txt b/contrib/bind9/doc/draft/draft-daigle-napstr-04.txt deleted file mode 100644 index fffa8a5..0000000 --- a/contrib/bind9/doc/draft/draft-daigle-napstr-04.txt +++ /dev/null @@ -1,1232 +0,0 @@ - - -Network Working Group L. Daigle -Internet-Draft A. Newton -Expires: August 15, 2004 VeriSign, Inc. - February 15, 2004 - - - Domain-based Application Service Location Using SRV RRs and the - Dynamic Delegation Discovery Service (DDDS) - draft-daigle-napstr-04.txt - -Status of this Memo - - This document is an Internet-Draft and is in full conformance with - all provisions of Section 10 of RFC2026. - - Internet-Drafts are working documents of the Internet Engineering - Task Force (IETF), its areas, and its working groups. Note that - other groups may also distribute working documents as Internet- - Drafts. - - Internet-Drafts are draft documents valid for a maximum of six months - and may be updated, replaced, or obsoleted by other documents at any - time. It is inappropriate to use Internet-Drafts as reference - material or to cite them other than as "work in progress." - - The list of current Internet-Drafts can be accessed at - http://www.ietf.org/ietf/1id-abstracts.txt. - - The list of Internet-Draft Shadow Directories can be accessed at - http://www.ietf.org/shadow.html. - - This Internet-Draft will expire on August 15, 2004. - -Copyright Notice - - Copyright (C) The Internet Society (2004). All Rights Reserved. - -Abstract - - This memo defines a generalized mechanism for application service - naming that allows service location without relying on rigid domain - naming conventions (so-called name hacks). The proposal defines a - Dynamic Delegation Discovery System (DDDS) Application to map domain - name, application service name, and application protocol to target - server and port, dynamically. - - - - - - - -Daigle & Newton Expires August 15, 2004 [Page 1] - -Internet-Draft draft-daigle-napstr-04 February 2004 - - -Table of Contents - - 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 - 2. Straightforward-NAPTR (S-NAPTR) Specification . . . . . . . 4 - 2.1 Key Terms . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 2.2 S-NAPTR DDDS Application Usage . . . . . . . . . . . . . . . 5 - 2.2.1 Ordering and Preference . . . . . . . . . . . . . . . . . . 5 - 2.2.2 Matching and non-Matching NAPTR Records . . . . . . . . . . 5 - 2.2.3 Terminal and Non-Terminal NAPTR Records . . . . . . . . . . 5 - 2.2.4 S-NAPTR and Successive Resolution . . . . . . . . . . . . . 6 - 2.2.5 Clients Supporting Multiple Protocols . . . . . . . . . . . 6 - 3. Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . 7 - 3.1 Guidelines for Application Protocol Developers . . . . . . . 7 - 3.1.1 Registration of application service and protocol tags . . . 7 - 3.1.2 Definition of conditions for retry/failure . . . . . . . . . 8 - 3.1.3 Server identification and handshake . . . . . . . . . . . . 8 - 3.2 Guidelines for Domain Administrators . . . . . . . . . . . . 8 - 3.3 Guidelines for Client Software Writers . . . . . . . . . . . 9 - 4. Illustrations . . . . . . . . . . . . . . . . . . . . . . . 9 - 4.1 Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 4.2 Service Discovery within a Domain . . . . . . . . . . . . . 10 - 4.3 Multiple Protocols . . . . . . . . . . . . . . . . . . . . . 10 - 4.4 Remote Hosting . . . . . . . . . . . . . . . . . . . . . . . 11 - 4.5 Sets of NAPTR RRs . . . . . . . . . . . . . . . . . . . . . 12 - 4.6 Sample sequence diagram . . . . . . . . . . . . . . . . . . 12 - 5. Motivation and Discussion . . . . . . . . . . . . . . . . . 14 - 5.1 So, why not just SRV records? . . . . . . . . . . . . . . . 15 - 5.2 So, why not just NAPTR records? . . . . . . . . . . . . . . 15 - 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . 16 - 7. Security Considerations . . . . . . . . . . . . . . . . . . 16 - 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17 - References . . . . . . . . . . . . . . . . . . . . . . . . . 17 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 18 - A. Application Service Location Application of DDDS . . . . . . 18 - A.1 Application Unique String . . . . . . . . . . . . . . . . . 18 - A.2 First Well Known Rule . . . . . . . . . . . . . . . . . . . 18 - A.3 Expected Output . . . . . . . . . . . . . . . . . . . . . . 18 - A.4 Flags . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 - A.5 Service Parameters . . . . . . . . . . . . . . . . . . . . . 19 - A.5.1 Application Services . . . . . . . . . . . . . . . . . . . . 19 - A.5.2 Application Protocols . . . . . . . . . . . . . . . . . . . 20 - A.6 Valid Rules . . . . . . . . . . . . . . . . . . . . . . . . 20 - A.7 Valid Databases . . . . . . . . . . . . . . . . . . . . . . 20 - B. Pseudo pseudocode for S-NAPTR . . . . . . . . . . . . . . . 20 - B.1 Finding the first (best) target . . . . . . . . . . . . . . 20 - B.2 Finding subsequent targets . . . . . . . . . . . . . . . . . 21 - Full Copyright Statement . . . . . . . . . . . . . . . . . . 23 - - - - -Daigle & Newton Expires August 15, 2004 [Page 2] - -Internet-Draft draft-daigle-napstr-04 February 2004 - - -1. Introduction - - This memo defines a generalized mechanism for application service - naming that allows service location without relying on rigid domain - naming conventions (so-called name hacks). The proposal defines a - Dynamic Delegation Discovery System (DDDS -- see [6]) Application to - map domain name, application service name, and application protocol - to target server and port, dynamically. - - As discussed in Section 5, existing approaches to using DNS records - to dynamically determining the current host for a given application - service are limited in terms of the use cases supported. To address - some of the limitations, this document defines a DDDS Application to - map service+protocol+domain to specific server addresses using both - NAPTR [7] and SRV ([5]) DNS resource records. This can be viewed as - a more general version of the use of SRV and/or a very restricted - application of the use of NAPTR resource records. - - The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", - "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this - document are to be interpreted as described in RFC2119 ([2]). - -2. Straightforward-NAPTR (S-NAPTR) Specification - - The precise details of the specification of this DDDS application are - given in Appendix A. This section defines the usage of the DDDS - application. - -2.1 Key Terms - - An "application service" is a generic term for some type of - application, indpendent of the protocol that may be used to offer it. - Each application service will be associated with an IANA-registered - tag. For example, instant messaging is a type of application - service, which can be implemented by many different application-layer - protocols, and the tag "IM" (used as an illustration here) could be - registered for it. - - An "application protocol" is used to implement the application - service. These are also associated with IANA-registered tags. In - the case where multiple transports are available for the application, - separate tags should be defined for each transport. - - The intention is that the combination of application service and - protocol tags should be specific enough that finding a known pair - (e.g., "IM:ProtC") is sufficient for a client to identify a server - with which it can communicate. - - - - -Daigle & Newton Expires August 15, 2004 [Page 3] - -Internet-Draft draft-daigle-napstr-04 February 2004 - - - Some protocols support multiple application services. For example, - LDAP is an application protocol, and can be found supporting various - services (e.g., "whitepages", "directory enabled networking", etc). - -2.2 S-NAPTR DDDS Application Usage - - As outlined in Appendix A, NAPTR records are used to store - application service+protocol information for a given domain. - Following the DDDS standard, these records are looked up, and the - rewrite rules (contained in the NAPTR records) are used to determine - the successive DNS lookups, until a desirable target is found. - - For the rest of this section, refer to the set of NAPTR resource - records for example.com shown in the figure below. - - example.com. - ;; order pref flags service regexp replacement - IN NAPTR 100 10 "" "WP:whois++" "" bunyip.example. - IN NAPTR 100 20 "s" "WP:ldap" "" _ldap._tcp.myldap.example.com. - IN NAPTR 200 10 "" "IM:protA" "" someisp.example. - IN NAPTR 200 30 "a" "IM:protB" "" myprotB.example.com. - - -2.2.1 Ordering and Preference - - A client retrieves all of the NAPTR records associated with the - target domain name (example.com, above). These are to be sorted in - terms of increasing ORDER, and increasing PREF within each ORDER. - -2.2.2 Matching and non-Matching NAPTR Records - - Starting with the first sorted NAPTR record, the client examines the - SERVICE field to find a match. In the case of the S-NAPTR DDDS - application, that means a SERVICE field that includes the tags for - the desired application service and a supported application protocol. - - If more than one NAPTR record matches, they are processed in - increasing sort order. - -2.2.3 Terminal and Non-Terminal NAPTR Records - - A NAPTR record with an empty FLAG field is "non-terminal". That is, - more NAPTR RR lookups are to be performed. Thus, to process a NAPTR - record with an empty FLAG field in S-NAPTR, the REPLACEMENT field is - used as the target of the next DNS lookup -- for NAPTR RRs. - - In S-NAPTR, the only terminal flags are "S" and "A". These are - called "terminal" NAPTR lookups because they denote the end of the - - - -Daigle & Newton Expires August 15, 2004 [Page 4] - -Internet-Draft draft-daigle-napstr-04 February 2004 - - - DDDS/NAPTR processing rules. In the case of an "S" flag, the - REPLACEMENT field is used as the target of a DNS query for SRV RRs, - and normal SRV processing is applied. In the case of an "A" flag, an - address record is sought for the REPLACEMENT field target (and the - default protocol port is assumed). - -2.2.4 S-NAPTR and Successive Resolution - - As shown in the example NAPTR RR set above, it is possible to have - multiple possible targets for a single application service+protocol - pair. These are to be pursued in order until a server is - successfully contacted or all possible matching NAPTR records have - been successively pursued to terminal lookups and servers contacted. - That is, a client must backtrack and attempt other resolution paths - in the case of failure. - - "Failure" is declared, and backtracking must be used when - - o the designated remote server (host and port) fail to provide - appropriate security credentials for the *originating* domain - - o connection to the designated remote server otherwise fails -- the - specifics terms of which are defined when an application protocol - is registered - - o the S-NAPTR-designated DNS lookup fails to yield expected results - -- e.g., no A RR for an "A" target, no SRV record for an "S" - target, or no NAPTR record with appropriate application service - and protocol for a NAPTR lookup. Except in the case of the very - first NAPTR lookup, this last is a configuration error: the fact - that example.com has a NAPTR record pointing to "bunyip.example" - for the "WP:Whois++" service and protocol means the administrator - of example.com believes that service exists. If bunyip.example - has no "WP:Whois++" NAPTR record, the application client MUST - backtrack and try the next available "WP:Whois++" option from - example.com. As there is none, the whole resolution fails. - - An application client first queries for the NAPTR RRs for the domain - of a named application service. The application client MUST select - one protocol to choose The PREF field of the NAPTR RRs may be used by - the domain administrator to The first DNS query is for the NAPTR RRs - in the original target domain (example.com, above). - -2.2.5 Clients Supporting Multiple Protocols - - In the case of an application client that supports more than one - protocol for a given application service, it MUST pursue S-NAPTR - resolution completely for one protocol before trying another.j It MAY - - - -Daigle & Newton Expires August 15, 2004 [Page 5] - -Internet-Draft draft-daigle-napstr-04 February 2004 - - - choose which protocol to try first based on its own preference, or - from the PREF ranking in the first set of NAPTR records (i.e., those - for the target named domain). However, the chosen protocol MUST be - listed in that first NAPTR RR set. - - That is, what the client MUST NOT do is start looking for one - protocol, observe that a successive NAPTR RR set supports another of - its preferred protocols, and continue the S-NAPTR resolution based on - that protocol. For example, even if someisp.example offers the "IM" - service with protocol "ProtB", there is no reason to believe it does - so on behalf of example.com (since there is no such pointer in - example.com's NAPTR RR set). - -3. Guidelines - -3.1 Guidelines for Application Protocol Developers - - The purpose of S-NAPTR is to provide application standards developers - with a more powerful framework (than SRV RRs alone) for naming - service targets, without requiring each application protocol (or - service) standard to define a separate DDDS application. - - Note that this approach is intended specifically for use when it - makes sense to associate services with particular domain names (e.g., - e-mail addresses, SIP addresses, etc). A non-goal is having all - manner of label mapped into domain names in order to use this. - - Specifically not addressed in this document is how to select the - domain for which the service+protocol is being sought. It is up to - other conventions to define how that might be used (e.g., instant - messaging standards can define what domain to use from IM URIs, how - to step down from foobar.example.com to example.com, and so on, if - that is applicable). - - Although this document proposes a DDDS application that does not use - all the features of NAPTR resource records, it does not mean to imply - that DNS resolvers should fail to implement all aspects of the NAPTR - RR standard. A DDDS application is a client use convention. - - The rest of this section outlines the specific elements that protocol - developers must determine and document in order to make use of S- - NAPTR. - -3.1.1 Registration of application service and protocol tags - - Application protocol developers that wish to make use of S-NAPTR must - make provision to register any relevant application service and - application protocol tags, as described in Section 6. - - - -Daigle & Newton Expires August 15, 2004 [Page 6] - -Internet-Draft draft-daigle-napstr-04 February 2004 - - -3.1.2 Definition of conditions for retry/failure - - One other important aspect that must be defined is the expected - behaviour for interacting with the servers that are reached via S- - NAPTR. Specifically, under what circumstances should the client - retry a target that was found via S-NAPTR? What should it consider a - failure that causes it to return to the S-NAPTR process to determine - the next serviceable target (a less preferred target)? - - For example, if the client gets a "connection refused" from a server, - should it retry for some (protocol-dependent) period of time? Or, - should it try the next-preferred target in the S-NAPTR chain of - resolution? Should it only try the next-preferred target if it - receives a protocol-specific permanent error message? - - The most important thing is to select one expected behaviour and - document it as part of the use of S-NAPTR. - - As noted earlier, failure to provide appropriate credentials to - identify the server as being authoritative for the original taret - domain is always considered a failure condition. - -3.1.3 Server identification and handshake - - As noted in Section 7, use of the DNS for server location increases - the importance of using protocol-specific handshakes to determine and - confirm the identity of the server that is eventually reached. - - Therefore, application protocol developers using S-NAPTR should - identify the mechanics of the expected identification handshake when - the client connects to a server found through S-NAPTR. - -3.2 Guidelines for Domain Administrators - - Although S-NAPTR aims to provide a "straightforward" application of - DDDS and use of NAPTR records, it is still possible to create very - complex chains and dependencies with the NAPTR and SRV records. - - Therefore, domain administrators are called upon to use S-NAPTR with - as much restraint as possible, while still achieving their service - design goals. - - The complete set of NAPTR, SRV and A RRs that are "reachable" through - the S-NAPTR process for a particular application service can be - thought of as a "tree". Each NAPTR RR retrieved points to more NAPTR - or SRV records; each SRV record points to several A record lookups. - Even though a particular client can "prune" the tree to use only - those records referring to application protocols supported by the - - - -Daigle & Newton Expires August 15, 2004 [Page 7] - -Internet-Draft draft-daigle-napstr-04 February 2004 - - - client, the tree could be quite deep, and retracing the tree to retry - other targets can become expensive if the tree has many branches. - - Therefore, - - o Fewer branches is better: for both NAPTR and SRV records, provide - different targets with varying preferences where appropriate - (e.g., to provide backup services, etc), but don't look for - reasons to provide more. - - o Shallower is better: avoid using NAPTR records to "rename" - services within a zone. Use NAPTR records to identify services - hosted elsewhere (i.e., where you cannot reasonably provide the - SRV records in your own zone). - - -3.3 Guidelines for Client Software Writers - - To properly understand DDDS/NAPTR, an implementor must read [6]. - However, the most important aspect to keep in mind is that, if one - target fails to work for the application, it is expected that the - application will continue through the S-NAPTR tree to try the (less - preferred) alternatives. - -4. Illustrations - -4.1 Use Cases - - The basic intended use cases for which S-NAPTR has been developed - are: - - o Service discovery within a domain. For example, this can be used - to find the "authoritative" server for some type of service within - a domain (see the specific example in Section 4.2). - - o Multiple protocols. This is increasingly common as new - application services are defined. This includes the case of - instant messaging (a service) which can be offered with multiple - protocols (see Section 4.3). - - o Remote hosting. Each of the above use cases applies within the - administration of a single domain. However, one domain operator - may elect to engage another organization to provide an application - service. See Section 4.4 for an example that cannot be served by - SRV records alone. - - - - - - -Daigle & Newton Expires August 15, 2004 [Page 8] - -Internet-Draft draft-daigle-napstr-04 February 2004 - - -4.2 Service Discovery within a Domain - - There are occasions when it is useful to be able to determine the - "authoritative" server for a given application service within a - domain. This is "discovery", because there is no a priori knowledge - as to whether or where the service is offered; it is therefore - important to determine the location and characteristics of the - offered service. - - For example, there is growing discussion of having a generic - mechanism for locating the keys or certificates associated with - particular application (servers) operated in (or for) a particular - domain. Here's a hypothetical case for storing application key or - certificate data for a given domain. The premise is that some - credentials registry (CredReg) service has been defined to be a leaf - node service holding the keys/certs for the servers operated by (or - for) the domain. Furthermore, it is assumed that more than one - protocol is available to provide the service for a particular domain. - This DDDS-based approach is used to find the CredReg server that - holds the information. - - Thus, the set of NAPTR records for thinkingcat.example might look - like this: - - thinkingcat.example. - ;; order pref flags service regexp replacement - IN NAPTR 100 10 "" "CREDREG:ldap:iris-beep" "" theserver.thinkingcat.example. - - Note that another domain, offering the same application service, - might offer it using a different set of application protocols: - - anotherdomain.example. - ;; order pref flags service regexp replacement - IN NAPTR 100 10 "" "CREDREG:iris-lw:iris-beep" "" foo.anotherdomain.example. - - -4.3 Multiple Protocols - - As it stands, there are several different protocols proposed for - offering "instant message" services. Assuming that "IM" was - registered as an application service, this DDDS application could be - used to determine the available services for delivering to a target. - - Two particular features of instant messaging should be noted: - - 1. gatewaying is expected to bridge communications across protocols - - 2. instant messaging servers are likely to be operated out of a - - - -Daigle & Newton Expires August 15, 2004 [Page 9] - -Internet-Draft draft-daigle-napstr-04 February 2004 - - - different domain than the instant messaging address, and servers - of different protocols may be offered by independent - organizations - - For example, "thinkingcat.example" may support its own servers for - the "ProtA" instant messaging protocol, but rely on outsourcing from - "example.com" for "ProtC" and "ProtB" servers. - - Using this DDDS-based approach, thinkingcat.example can indicate a - preference ranking for the different types of servers for the instant - messaging service, and yet the out-sourcer can independently rank the - preference and ordering of servers. This independence is not - achievable through the use of SRV records alone. - - Thus, to find the IM services for thinkingcat.example, the NAPTR - records for thinkingcat.example are retrieved: - - thinkingcat.example. - ;; order pref flags service regexp replacement - IN NAPTR 100 10 "s" "IM:ProtA" "" _ProtA._tcp.thinkingcat.example. - IN NAPTR 100 20 "s" "IM:ProtB" "" _ProtB._tcp.example.com. - IN NAPTR 100 30 "s" "IM:ProtC" "" _ProtC._tcp.example.com. - - and then the administrators at example.com can manage the preference - rankings of the servers they use to support the ProtB service: - - _ProtB._tcp.example.com. - ;; Pref Weight Port Target - IN SRV 10 0 10001 bigiron.example.com - IN SRV 20 0 10001 backup.im.example.com - IN SRV 30 0 10001 nuclearfallout.australia-isp.example - - -4.4 Remote Hosting - - In the Instant Message hosting example in Section 4.3, the service - owner (thinkingcat.example) had to host pointers to the hosting - service's SRV records in the thinkingcat.example domain. - - A better way to approach this is to have one NAPTR RR in the - thinkingcat.example domain pointing to all the hosted services, and - the hosting domain has NAPTR records for each service to map them to - whatever local hosts it chooses (and may change from time to time). - - - - - - - - -Daigle & Newton Expires August 15, 2004 [Page 10] - -Internet-Draft draft-daigle-napstr-04 February 2004 - - - thinkingcat.example. - ;; order pref flags service regexp replacement - IN NAPTR 100 10 "s" "IM:ProtA" "" _ProtA._tcp.thinkingcat.example. - IN NAPTR 100 20 "" "IM:ProtB:ProtC" "" thinkingcat.example.com. - - - and then the administrators at example.com can break out the - individual application protocols and manage the preference rankings - of the servers they use to support the ProtB service (as before): - - thinkingcat.example.com. - ;; order pref flags service regexp replacement - IN NAPTR 100 10 "s" "IM:ProtC" "" _ProtC._tcp.example.com. - IN NAPTR 100 20 "s" "IM:ProtB" "" _ProtB._tcp.example.com. - - - - _ProtC._tcp.example.com. - ;; Pref Weight Port Target - IN SRV 10 0 10001 bigiron.example.com - IN SRV 20 0 10001 backup.im.example.com - IN SRV 30 0 10001 nuclearfallout.australia-isp.example - - -4.5 Sets of NAPTR RRs - - Note that the above sections assumed that there was one service - available (via S-NAPTR) per domain. Often, that will not be the - case. Assuming thinkingcat.example had the CredReg service set up as - described in Section 4.2 and the instant messaging service set up as - described in Section 4.4, then a client querying for the NAPTR RR set - from thinkingcat.com would get the following answer: - - thinkingcat.example. - ;; order pref flags service regexp replacement - IN NAPTR 100 10 "s" "IM:ProtA" "" _ProtA._tcp.thinkingcat.example. - IN NAPTR 100 20 "" "IM:ProtB:ProtC:" "" thinkingcat.example.com. - IN NAPTR 200 10 "" "CREDREG:ldap:iris-beep" "" bouncer.thinkingcat.example. - - Sorting them by increasing "ORDER", the client would look through the - SERVICE strings to determine if there was a NAPTR RR that matched the - application service it was looking for, with an application protocol - it could use. The first (lowest PREF) record that so matched is the - one the client would use to continue. - -4.6 Sample sequence diagram - - Consider the example in Section 4.3. Visually, the sequence of steps - - - -Daigle & Newton Expires August 15, 2004 [Page 11] - -Internet-Draft draft-daigle-napstr-04 February 2004 - - - required for the client to reach the final server for a "ProtB" - service for IM for the thinkingcat.example domain is as follows: - - - Client NS for NS for - thinkingcat.example example.com backup.im.example.com - | | | - 1 -------->| | | - 2 <--------| | | - 3 ------------------------------>| | - 4 <------------------------------| | - 5 ------------------------------>| | - 6 <------------------------------| | - 7 ------------------------------>| | - 8 <------------------------------| | - 9 ------------------------------------------------->| - 10 <-------------------------------------------------| - 11 ------------------------------------------------->| - 12 <-------------------------------------------------| - (...) - - - - 1. the name server (NS) for thinkingcat.example is reached with a - request for all NAPTR records - - 2. the server responds with the NAPTR records shown in Section 4.3. - - 3. the second NAPTR record matches the desired criteria; that has an - "s" flag and a replacement fields of "_ProtB._tcp.example.com". - So, the client looks up SRV records for that target, ultimately - making the request of the NS for example.com. - - 4. the response includes the SRV records listed in Section 4.3. - - 5. the client attempts to reach the server with the lowest PREF in - the SRV list -- looking up the A record for the SRV record's - target (bigiron.example.com). - - 6. the example.com NS responds with an error message -- no such - machine! - - 7. the client attempts to reach the second server in the SRV list, - and looks up the A record for backup.im.example.com - - 8. the client gets the A record with the IP address for - backup.im.example.com from example.com's NS. - - - - -Daigle & Newton Expires August 15, 2004 [Page 12] - -Internet-Draft draft-daigle-napstr-04 February 2004 - - - 9. the client connects to that IP address, on port 10001 (from the - SRV record), using ProtB over tcp. - - 10. the server responds with an "OK" message. - - 11. the client uses ProtB to challenge that this server has - credentials to operate the service for the original domain - (thinkingcat.example) - - 12. the server responds, and the rest is IM. - - -5. Motivation and Discussion - - Increasingly, application protocol standards are using domain names - to identify server targets, and stipulating that clients should look - up SRV resource records to determine the host and port providing the - server. This enables a distinction between naming an application - service target and actually hosting the server. It also increases - flexibility in hosting the target service: - - o the server may be operated by a completely different organization - without having to list the details of that organization's DNS - setup (SRVs) - - o multiple instances can be set up (e.g., for load balancing or - secondaries) - - o it can be moved from time to time without disrupting clients' - access, etc. - - This is quite useful, but Section 5.1 outlines some of the - limitations inherent in the approach. - - That is, while SRV records can be used to map from a specific service - name and protocol for a specific domain to a specific server, SRV - records are limited to one layer of indirection, and are focused on - server administration rather than on application naming. And, while - the DDDS specification and use of NAPTR allows multiple levels of - redirection before locating the target server machine with an SRV - record, this proposal requires only a subset of NAPTR strictly bound - to domain names, without making use of the REGEXP field of NAPTR. - These restrictions make the client's resolution process much more - predictable and efficient than with some potential uses of NAPTR - records. This is dubbed "S-NAPTR" -- a "S"traightforward use of - NAPTR records. - - - - - -Daigle & Newton Expires August 15, 2004 [Page 13] - -Internet-Draft draft-daigle-napstr-04 February 2004 - - -5.1 So, why not just SRV records? - - An expected question at this point is: this is so similar in - structure to SRV records, why are we doing this with DDDS/NAPTR? - - Limitations of SRV include: - - o SRV provides a single layer of indirection -- the outcome of an - SRV lookup is a new domain name for which the A RR is to be found. - - o the purpose of SRV is focused on individual server administration, - not application naming: as stated in [5] "The SRV RR allows - administrators to use several servers for a single domain, to move - services from host to host with little fuss, and to designate some - hosts as primary servers for a service and others as backups." - - o target servers by "service" (e.g., "ldap") and "protocol" (e.g., - "tcp") in a given domain. The definition of these terms implies - specific things (e.g., that protocol should be one of UDP or TCP) - without being precise. Restriction to UDP and TCP is insufficient - for the uses described here. - - The basic answer is that SRV records provide mappings from protocol - names to host and port. The use cases described herein require an - additional layer -- from some service label to servers that may in - fact be hosted within different administrative domains. We could - tweak SRV to say that the next lookup could be something other than - an address record, but that is more complex than is necessary for - most applications of SRV. - -5.2 So, why not just NAPTR records? - - That's a trick question. NAPTR records cannot appear in the wild -- - see [6]. They must be part of a DDDS application. - - The purpose here is to define a single, common mechanism (the DDDS - application) to use NAPTR when all that is desired is simple DNS- - based location of services. This should be easy for applications to - use -- some simple IANA registrations and it's done. - - Also, NAPTR has very powerful tools for expressing "rewrite" rules. - That power (==complexity) makes some protocol designers and service - administrators nervous. The concern is that it can translate into - unintelligible, noodle-like rule sets that are difficult to test and - administer. - - This proposed DDDS application specifically uses a subset of NAPTR's - abilities. Only "replacement" expressions are allowed, not "regular - - - -Daigle & Newton Expires August 15, 2004 [Page 14] - -Internet-Draft draft-daigle-napstr-04 February 2004 - - - expressions". - -6. IANA Considerations - - This document calls for 2 IANA registries: one for application - service tags, and one for application protocol tags. - - Application service and protocol tags should be defined in an RFC - (unless the "x-" experimental form is used, in which case they are - unregistered). There are no restrictions placed on the tags other - than that they must conform with the syntax defined below (Appendix - A.5). The IANA registries should list the tags and the RFC that - defines their use. - -7. Security Considerations - - The security of this approach to application service location is only - as good as the security of the DNS servers along the way. If any of - them is compromised, bogus NAPTR and SRV records could be inserted to - redirect clients to unintended destinations. This problem is hardly - unique to S-NAPTR (or NAPTR in general). - - To protect against DNS-vectored attacks, applications should define - some form of end-to-end authentication to ensure that the correct - destination has been reached. Many application protocols such as - HTTPS, BEEP, IMAP, etc... define the necessary handshake mechansims - to accomplish this task. - - The basic mechanism works in the following way: - - 1. During some portion of the protocol handshake, the client sends - to the server the original name of the desired destination (i.e. - no transformations that may have resulted from NAPTR - replacements, SRV targets, or CNAME changes). In certain cases - where the application protocol does not have such a feature but - TLS may be used, it is possible to use the "server_name" TLS - extension. - - 2. The server sends back to the client a credential with the - appropriate name. For X.509 certificates, the name would either - be in the subjectDN or subjectAltName fields. For Kerberos, the - name would be a service principle name. - - 3. Using the matching semantics defined by the application protocol, - the client compares the name in the credential with the name sent - to the server. - - 4. If the names match, there is reasonable assurance that the - - - -Daigle & Newton Expires August 15, 2004 [Page 15] - -Internet-Draft draft-daigle-napstr-04 February 2004 - - - correct end point has been reached. - - It is important to note that this document does not define either the - handshake mechanism, the specific credenential naming fields, nor the - name matching semantics. Definitions of S-NAPTR for particular - application protocols MUST define these. - -8. Acknowledgements - - Many thanks to Dave Blacka, Patrik Faltstrom, Sally Floyd for - discussion and input that has (hopefully!) provoked clarifying - revisions of this document. - -References - - [1] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource - Identifiers (URI): Generic Syntax", RFC 2396, August 1998. - - [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement - Levels", BCP 14, RFC 2119, March 1997. - - [3] Crocker, D. and P. Overell, "Augmented BNF for Syntax - Specifications: ABNF", RFC 2234, November 1997. - - [4] Eastlake, D., "Domain Name System Security Extensions", RFC - 2535, March 1999. - - [5] Gulbrandsen, A., Vixie, P. and L. Esibov, "A DNS RR for - specifying the location of services (DNS SRV)", RFC 2782, - February 2000. - - [6] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part - One: The Comprehensive DDDS", RFC 3401, October 2002. - - [7] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part - Three: The Domain Name System (DNS) Database", RFC 3403, October - 2002. - - [8] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part - Four: The Uniform Resource Identifiers (URI)", RFC 3404, October - 2002. - - - - - - - - - - -Daigle & Newton Expires August 15, 2004 [Page 16] - -Internet-Draft draft-daigle-napstr-04 February 2004 - - -Authors' Addresses - - Leslie Daigle - VeriSign, Inc. - 21355 Ridgetop Circle - Dulles, VA 20166 - US - - EMail: leslie@verisignlabs.com; leslie@thinkingcat.com - - - Andrew Newton - VeriSign, Inc. - 21355 Ridgetop Circle - Dulles, VA 20166 - US - - EMail: anewton@verisignlabs.com - -Appendix A. Application Service Location Application of DDDS - - This section defines the DDDS application, as described in [6]. - -A.1 Application Unique String - - The Application Unique String is domain label for which an - authoritative server for a particular service is sought. - -A.2 First Well Known Rule - - The "First Well Known Rule" is identity -- that is, the output of the - rule is the Application Unique String, the domain label for which the - authoritative server for a particular service is sought. - -A.3 Expected Output - - The expected output of this Application is the information necessary - to connect to authoritative server(s) (host, port, protocol) for an - application service within a given a given domain. - -A.4 Flags - - This DDDS Application uses only 2 of the Flags defined for the - URI/URN Resolution Application ([8]): "S" and "A". No other Flags - are valid. - - Both are for terminal lookups. This means that the Rule is the last - one and that the flag determines what the next stage should be. The - - - -Daigle & Newton Expires August 15, 2004 [Page 17] - -Internet-Draft draft-daigle-napstr-04 February 2004 - - - "S" flag means that the output of this Rule is a domain label for - which one or more SRV [5] records exist. "A" means that the output - of the Rule is a domain name and should be used to lookup address - records for that domain. - - Consistent with the DDDS algorithm, if the Flag string is empty the - next lookup is for another NAPTR record (for the replacement target). - -A.5 Service Parameters - - Service Parameters for this Application take the form of a string of - characters that follow this ABNF ([3]): - - service-parms = [ [app-service] *(":" app-protocol)] - app-service = experimental-service / iana-registered-service - app-protocol = experimental-protocol / iana-registered-protocol - experimental-service = "x-" 1*30ALPHANUMSYM - experimental-protocol = "x-" 1*30ALPHANUMSYM - iana-registered-service = ALPHA *31ALPHANUMSYM - iana-registered-protocol = ALPHA *31ALPHANUM - ALPHA = %x41-5A / %x61-7A ; A-Z / a-z - DIGIT = %x30-39 ; 0-9 - SYM = %x2B / %x2D / %x2E ; "+" / "-" / "." - ALPHANUMSYM = ALPHA / DIGIT / SYM - ; The app-service and app-protocol tags are limited to 32 - ; characters and must start with an alphabetic character. - ; The service-parms are considered case-insensitive. - - Thus, the Service Parameters may consist of an empty string, just an - app-service, or an app-service with one or more app-protocol - specifications separated by the ":" symbol. - - Note that this is similar to, but not the same as the syntax used in - the URI DDDS application ([8]). The DDDS DNS database requires each - DDDS application to define the syntax of allowable service strings. - The syntax here is expanded to allow the characters that are valid in - any URI scheme name (see [1]). Since "+" (the separator used in the - RFC3404 service parameter string) is an allowed character for URI - scheme names, ":" is chosen as the separator here. - -A.5.1 Application Services - - The "app-service" must be a registered service [this will be an IANA - registry; this is not the IANA port registry, because we want to - define services for which there is no single protocol, and we don't - want to use up port space for nothing]. - - - - - -Daigle & Newton Expires August 15, 2004 [Page 18] - -Internet-Draft draft-daigle-napstr-04 February 2004 - - -A.5.2 Application Protocols - - The protocol identifiers that are valid for the "app-protocol" - production are any standard, registered protocols [IANA registry - again -- is this the list of well known/registered ports?]. - -A.6 Valid Rules - - Only substitution Rules are permitted for this application. That is, - no regular expressions are allowed. - -A.7 Valid Databases - - At present only one DDDS Database is specified for this Application. - [7] specifies a DDDS Database that uses the NAPTR DNS resource record - to contain the rewrite rules. The Keys for this database are encoded - as domain-names. - - The First Well Known Rule produces a domain name, and this is the Key - that is used for the first lookup -- the NAPTR records for that - domain are requested. - - DNS servers MAY interpret Flag values and use that information to - include appropriate NAPTR, SRV or A records in the Additional - Information portion of the DNS packet. Clients are encouraged to - check for additional information but are not required to do so. See - the Additional Information Processing section of [7] for more - information on NAPTR records and the Additional Information section - of a DNS response packet. - -Appendix B. Pseudo pseudocode for S-NAPTR - -B.1 Finding the first (best) target - - Assuming the client supports 1 protocol for a particular application - service, the following pseudocode outlines the expected process to - find the first (best) target for the client, using S-NAPTR. - - - target = [initial domain] - naptr-done = false - - while (not naptr-done) - { - NAPTR-RRset = [DNSlookup of NAPTR RRs for target] - [sort NAPTR-RRset by ORDER, and PREF within each ORDER] - rr-done = false - cur-rr = [first NAPTR RR] - - - -Daigle & Newton Expires August 15, 2004 [Page 19] - -Internet-Draft draft-daigle-napstr-04 February 2004 - - - while (not rr-done) - if ([SERVICE field of cur-rr contains desired application - service and application protocol]) - rr-done = true - target= [REPLACEMENT target of NAPTR RR] - else - cur-rr = [next rr in list] - - if (not empty [FLAG in cur-rr]) - naptr-done = true - } - - port = -1 - - if ([FLAG in cur-rr is "S"]) - { - SRV-RRset = [DNSlookup of SRV RRs for target] - [sort SRV-RRset based on PREF] - target = [target of first RR of SRV-RRset] - port = [port in first RR of SRV-RRset] - } - - ; now, whether it was an "S" or an "A" in the NAPTR, we - ; have the target for an A record lookup - - host = [DNSlookup of target] - - return (host, port) - - - -B.2 Finding subsequent targets - - The pseudocode in Appendix B is crafted to find the first, most - preferred, host-port pair for a particular application service an - protocol. If, for any reason, that host-port pair did not work - (connection refused, application-level error), the client is expected - to try the next host-port in the S-NAPTR tree. - - The pseudocode above does not permit retries -- once complete, it - sheds all context of where in the S-NAPTR tree it finished. - Therefore, client software writers could - - o entwine the application-specific protocol with the DNS lookup and - RRset processing described in the pseudocode and continue the S- - NAPTR processing if the application code fails to connect to a - located host-port pair; - - - - -Daigle & Newton Expires August 15, 2004 [Page 20] - -Internet-Draft draft-daigle-napstr-04 February 2004 - - - o use callbacks for the S-NAPTR processing; - - o use an S-NAPTR resolution routine that finds *all* valid servers - for the required application service and protocol from the - originating domain, and provides them in sorted order for the - application to try in order. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Daigle & Newton Expires August 15, 2004 [Page 21] - -Internet-Draft draft-daigle-napstr-04 February 2004 - - -Full Copyright Statement - - Copyright (C) The Internet Society (2004). All Rights Reserved. - - This document and translations of it may be copied and furnished to - others, and derivative works that comment on or otherwise explain it - or assist in its implementation may be prepared, copied, published - and distributed, in whole or in part, without restriction of any - kind, provided that the above copyright notice and this paragraph are - included on all such copies and derivative works. However, this - document itself may not be modified in any way, such as by removing - the copyright notice or references to the Internet Society or other - Internet organizations, except as needed for the purpose of - developing Internet standards in which case the procedures for - copyrights defined in the Internet Standards process must be - followed, or as required to translate it into languages other than - English. - - The limited permissions granted above are perpetual and will not be - revoked by the Internet Society or its successors or assigns. - - This document and the information contained herein is provided on an - "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING - TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING - BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION - HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF - MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. - -Acknowledgement - - Funding for the RFC Editor function is currently provided by the - Internet Society. - - - - - - - - - - - - - - - - - - - -Daigle & Newton Expires August 15, 2004 [Page 22] - |
